By Irene Klotz

CAPE CANAVERAL, Fla., May 9 (Reuters) - Seven astronauts climbed inside the space shuttle Discovery on Friday as part of a dress rehearsal for a May 31 mission to deliver a Japanese laboratory to the International Space Station.

Five of the seven have not flown in space before and have been spending more time in simulators than real spaceships.

Pilot Ken Ham said he had to look closely at two adjacent shuttle launch pads at the Kennedy Space Center in Florida to find Discovery, which is partly wrapped in a protective metal structure.

"I think this is a sign of a being a rookie," he joked.

NASA called off the countdown with a few seconds left on the clock so the crew could practice an emergency evacuation.

Managers plan to meet next week to review preparations. With no major technical issues pending, NASA is expected to clear the shuttle for launch on May 31. Two days later, it will arrive at the station to install Japan's Kibo laboratory.

The U.S. space agency has 10 missions remaining to complete construction of the $100 billion outpost, a project of 16 member nations. It also plans to service the Hubble Space Telescope before the shuttle fleet is retired in 2010. (Editing by Jim Loney and Alan Elsner)

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